Understanding Seasonal Affective Disorder (SAD): Symptoms, Causes & Practical Ways to Cope

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As the days grow shorter and temperatures drop, many people begin to notice a shift in their mood. Feeling a little less motivated, more melancholy (than usual) or craving an extra hour of sleep during the colder months isn’t unusual.

But for some, this seasonal shift becomes something much deeper and more disruptive – a form of depression known as Seasonal Affective Disorder (SAD). Often referred to as “winter depression,” or “winter blues,” SAD affects millions of people each year.

And the impacts of this seemingly innocuous condition are not to be taken lightly. According to a number of leading health institutions (such as John’s Hopkins and Cleveland Clinc), SAD can impede productivity, decrease energy levels, deteriorate emotional wellness while also exacerbating anxiety and depression.

This comprehensive guide explores what Seasonal Affective Disorder is, common symptoms, why it happens and evidence-based strategies to help you manage and navigate the darker months with more ease and resilience.

What is Seasonal Affective Disorder?

Seasonal Affective Disorder (SAD) is a type of depression that follows a predictable seasonal pattern, typically beginning in late fall or early winter and subsiding in spring or early summer. While winter-onset SAD is the most common form, a smaller percentage of people experience summer-onset SAD, where symptoms appear during warmer months.

SAD is recognised as a subtype of major depressive disorder or bipolar disorder, depending on the individual’s broader mental-health history. The distinguishing feature is seasonality – symptoms emerge regularly during specific times of the year.

Who is most at risk of SAD?

Certain groups are more likely to develop SAD:

• People living far from the equator, where daylight hours change dramatically

• Individuals with a personal or family history of depression

• Young adults, especially women

• People with vitamin D deficiency (best vitamin D supplement)

• Those with existing mood disorders, such as bipolar disorder

Even if you’ve never experienced depression before, you can still develop SAD.

What causes Seasonal Affective Disorder?

While the exact causes of SAD aren’t fully understood, researchers believe several biological and environmental factors play a role:

1. Reduced sunlight exposure

Decreased daylight during fall and winter disrupts the body's internal clock (circadian rhythm), contributing to feelings of depression, fatigue and sleep disturbances. (This explains why SAD is more prevalent in Northern Hemisphere countries.)

2. Serotonin levels drop

Serotonin – a neurotransmitter that influences mood and wellbeing – often decreases when sunlight exposure decreases. Low serotonin is linked to increased risk of winter depression and other mood disorders.

3. Melatonin disruption

Melatonin, the hormone responsible for regulating sleep-wake cycles, can be overproduced during darker months. This contributes to excessive sleepiness, low energy and sluggishness commonly associated with SAD.

4. Vitamin D deficiency

The body produces vitamin D when exposed to sunlight. During winter, levels tend to drop, which may impact serotonin activity and worsen SAD symptoms.

5. Genetic and environmental factors

Family history, hormone regulation, and individual brain chemistry all play roles in determining who develops seasonal affective disorder.

Seasonal Affective Disorder symptoms

The symptoms of SAD resemble those of major depressive disorder but follow a seasonal pattern. They range from mild to severe and can significantly disrupt daily functioning. What follows is a list of the most common winter-onset SAD symptoms:

Emotional and psychological symptoms

• Persistent low mood lasting most of the day

• Feeling hopeless, sad, or tearful

• Increased irritability or anxiety

• Loss of interest in activities once enjoyed

• Difficulty concentrating

• Feelings of worthlessness or guilt

Physical and behavioural symptoms

• Increased sleep (hypersomnia)

• Low energy and chronic fatigue

• Increased appetite, particularly for carbohydrates

• Weight gain

• Social withdrawal or “hibernation behaviour”

• Difficulty getting out of bed in the morning

Summer-onset SAD symptoms

Though less common, symptoms may include:

• Insomnia

• Loss of appetite

• Unintended weight loss

• Agitation or anxiety

• Increased irritability

If symptoms interfere with daily functioning, it’s important to seek professional medical support.

How is Seasonal Affective Disorder diagnosed?

It’ll come as a relief to know that diagnosing Seasonal Affective Disorder is a relatively straightforward process. A healthcare provider (such as your GP) or mental-health professional can diagnose SAD. The methods they use are typically non-invasive and can be completed in a single session. Such methods include:

• A review of your symptoms and their seasonal pattern

• A mental-health evaluation or questionnaire

• Medical tests to rule out other causes such as thyroid issues or vitamin deficiencies

To be diagnosed with SAD, a person must experience symptoms during the same season for at least two consecutive years.

How to manage Seasonal Affective Disorder

The good news: Seasonal Affective Disorder is highly treatable, and many people find significant relief through a combination of lifestyle adjustments, therapeutic interventions and self-care practices.

Below are some of the most effective strategies.

1. Light therapy (phototherapy)

One of the most common and effective treatments for SAD is light therapy, which involves sitting near a bright light box that mimics natural sunlight. The device emits 10,000 lux of light and is used for about 20–30 minutes each morning.

Benefits of light therapy

• Regulates circadian rhythm

• Improves serotonin levels

• Increases energy and alertness

• Reduces depressive symptoms

Many people experience improvement within 1–2 weeks. Always choose a medically approved light therapy box and follow safety guidelines.

2. Cognitive Behavioural Therapy (CBT)

CBT, particularly CBT-SAD (a version tailored for seasonal depression), is a proven method for managing symptoms. It helps by:

• Challenging negative thought patterns

• Building healthier coping strategies

• Improving emotional resilience year-round

CBT is often as effective as light therapy and may have longer-lasting benefits.

3. Vitamin D supplementation

Given the strong link between vitamin D deficiency and winter depression, supplementation may help alleviate symptoms – especially for individuals who live in northern regions or spend little time outdoors.

Always check your levels with a healthcare provider before supplementing. I use Nature Provides because it contains only natural ingredients.

4. Medication (antidepressants)

For moderate to severe cases, a doctor may prescribe antidepressants such as SSRIs to regulate serotonin levels. These medications can be started before winter if symptoms reliably recur each year.

5. Improve sleep hygiene

A disrupted sleep cycle affects more than just our mood. It is closely tied to a wide range of mental health challenges (in addition to a startling number of non-communicable diseases). The importance and impact of sleep on mental health are highlighted in the book, Why We Sleep.

The author outlines a wealth of research showing a ‘strong relationship’ between ‘poor sleep hygiene’ and the exacerbation of anxiety, bipolar, chronic stress, depression and, of course, SAD.

So, anyone who is struggling with the conditions outlined above, ought to begin improving the quality of their sleep. Thankfully, there are several simple yet effective methods that can make a significant difference. Here is a selection of tips from Why We Sleep:

• Going to bed and waking at the same time daily (“Stick to a sleep schedule”)

• Limiting screen time before bed (shut off devices one hour before tucking up)

• Sleeping in a dark, cool environment

• Getting morning sunlight exposure when possible

• Exercise and activity (but not too late)

• Avoid caffeine and nicotine (and vaping)

• Avoid consuming alcohol

• Don’t take naps or midday siestas

• Engage in relaxing activities such as reading, journaling and/or meditation (try these meditation exercises)

6. Prioritise physical activity

Physical activity and exercise are both natural mood boosters and scores of studies show that they help mitigate low mood and depression. In his excellent book, Exercised, Professor Daniel Lieberman reminds us that exercise stimulates ‘mood-enhancing chemicals in the brain’ such as (naturally occurring) opioids, endorphins and endocannabinoids – a curious compound that shares a similar molecular makeup as marijuana.

Shaking up this chemical cocktail confers a ‘diverse and varied’ range of mental health benefits. According to Lieberman, engaging in regular physical activity reduces stress and anxiety while also dampening the severity of depression.

In addition to boosting mood, exercise also stimulates the secretion of BDNF (brain-derived neurotropic factor), a chemical that is instrumental in the wonderous process of ‘neurogenesis’ – the birthing of new neurons. Studies have shown that elevated baseline levels of BDNF correlates with denser brain regions, specifically in the hippocampus (the memory centre of the brain), improved cognition and memory retention and the reduced progression of ‘age-related cognitive decline.’  

Beneficial activities include

• Aerobic exercise (jogging, cycling, rowing, swimming)

• Brisk walking

• Yoga

• Strength training

• Dancing

• Winter sports like skiing or ice skating

Even 20–30 minutes per day can significantly reduce SAD symptoms.

7. Get outside daily

Even on cloudy days, outdoor light is far brighter than indoor lighting. Exposure to natural light – even for short periods – can help regulate sleep patterns and improve serotonin production. Furthermore, as I show in my article on Nature Therapies, studies show that immersing yourself in greens spaces induces a calming effect while also boosting positivity. Consider participating in:

• Morning walks

• Sitting near a window

• Taking breaks outside during work

• Taking walks in green spaces

8. Maintain a social routine

Social withdrawal is common in seasonal depression, but staying connected can reduce isolation and improve mood. Ideas include:

• Joining a hobby group

• Planning weekly meet-ups

• Volunteering

• Scheduling check-ins with friends and family

9. Nourish your body with a balanced diet

Comfort foods may be tempting, especially carbohydrates and sweets, but maintaining a balanced diet supports emotional stability and energy levels. (For a comprehensive insight into the impacts of diet on mental and physical health, see Dr Greger's How Not To Age.)

Nutrient-dense foods to prioritise:

• Leafy greens

• Berries and citrus fruits

• Lean protein

• Omega-3 rich foods like salmon and walnuts

• Whole grains

Staying hydrated is equally important.

10. Practice mindfulness and stress reduction techniques

Meditation, deep breathing and mindfulness-based stress reduction (MBSR) can help manage anxiety, low mood and rumination. You could try:

• Guided meditation apps

• Breathing exercises

• Journaling

• Gentle stretching

• Gratitude lists

Even small daily practices can build emotional resilience over time.

When to seek professional help

While mild SAD symptoms can often be managed with lifestyle changes, professional help is essential if:

• You feel hopeless or persistently depressed

• Symptoms interfere with your work, relationships, or daily functioning

• You experience thoughts of self-harm

• Home strategies aren’t helping

A mental-health professional can provide personalised treatment, therapy and support.

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Final thoughts

Seasonal Affective Disorder is more than “winter blues” – it’s a real, biological condition that can significantly impact mental and emotional wellbeing. But with understanding, awareness, and proactive strategies, SAD is highly manageable. From light therapy and CBT to daily habits that support mood and energy, there are more tools than ever to help you reclaim your motivation, joy, and balance during the darker months.

If you suspect you may be dealing with SAD, reach out to a healthcare professional and explore the treatment options that align best with your lifestyle and needs. You deserve support, and brighter days – both literal and emotional – are ahead.

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References

Lieberman, D (2020) Exercised: The Science of Physical Activity, Rest and Health. Penguin. New York. (Quotes above can be found on pages 223, 334 and 335.)

Walker, M (2017) Why We Sleep. Penguin. New York.

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bout Dr Laura Allen –

A Chartered Psychologist & Integrative Therapist, Dr Allen specialises in a broad range of therapeutic methods. She is a published author of numerous research papers and Interactive Courses in the field of Psychology. Dr. Allen works one-to-one with clients and supervises other practitioners. She is also a proud member of the British Psychological Society assessment team supporting psychologists in training.